Humidifiers and Dehumidifiers - No Voltage detected on Solenoid Valve

I no longer hear any clicking noise even i turn to TEST mode on my Aprilaire 600. At first I thought the humidistat might have gone bad. However, when I used a voltage meter mearsuing it, it did have ~27 vac going into the humidistat. It did not have any voltage coming out to the solenoid valve. When I unpluged the wires to the solenoid valve and measured it, I was able to detect ~20vac coming out of the humidistat. Does that mean I need to replace the solenoid valve? Thanks.

Yes, if you are getting power to the valve, then it needs to be replaced.

I replaced the valve but it still does not work. I ended up just bypassing the humidistat and I am able to see water come out from the humidier when heat is called. I guess I also need to replace the humidstat. My Aprilaire 600 is almost 5 years old. Is it typical that valve and humidstat go bad?

Any parts and controls can go out any time on units. So if you bypassed the control and the valve works then it has to be just in that control. just dirt or age can make things go out.;)

You can get a basic honeywell humidistat at Home Depot, but the hole may not be the same if the humidistat is cut into the return ductwork.

I replaced the humidistat. My humidifer is working now. Thanks.